Laser soldering of large lenses for applications in high-power laser systems

Within an European Space Agency (ESA) Basic Technology Research Programme (TRP) funded project a laser-based soldering technology was evaluated for a low-stress bonding of large (>100 mm diameter) lenses, e.g. made of Calcium Fluoride (CaF2), within mounts. Objective of the activity was to overcome limitations of traditional clamping and adhesive bonding technologies with respect to stress and long-term stability in harsh and high power environments, by applying a anorganic-metallic bonding agent, and a localized, minimal impact laser-based soldering technology, the so-called Solderjet Bumping (SJB). Fused Silica and CaF2 lens dummies were processed, respective mounts in CTE-matching materials incorporated flexures to minimize operational and non-operation environmental conditions thermo-mechanical stress. Throughout the whole process chain of assembly and testing surface P-V deviations <100 nm, birefringence changes <10 nm, and position changes <1 micron where measured. The results enable applications of the technology for high power systems e.g. in laser material processing and fusion energy creation.